FIG. 8 shows a traditional starter motor for an engine of a lawn mower. The starter motor comprises an electric motor 1, a reduction gearbox 2 connected to a shaft of the motor 1, an output shaft 3 of the gearbox 2, and a pinion 4 mounted on the output shaft 3. When the motor 1 is operated, the output shaft 3 is rotated to thereby drive the pinion 4. The pinion illustrated is an inertia type pinion which relies on the inertia of the pinion and a helical spline connection between the output shaft and the pinion to move the pinion axially along the output shaft 3 to engage a flywheel 5 of the engine 6 when the starter motor is turned on. Consequently, the flywheel 5 and the engine shaft 7 to which the flywheel is fixed are rotated to thereby start the engine 6. After the engine 6 starts, the speed of the flywheel 5 will increase and the pinion 4 will disengage from the flywheel 5. The flywheel 5 has an induction magnet installed at the outer surface thereof. An induction coil 9 is located near the flywheel 5 for cooperating with the induction magnet to generate power for an ignition system. A fan 8 may be formed on the flywheel to provide cooling for the engine.
However, the above starter motor comprises a motor, gearbox and pinion installed outside of the flywheel where it is vulnerable to external damage. The starter motor has a complicated structure and occupies space.